Compressors and expansion machines of the worm and pinion type

ABSTRACT

A compressor or expansion machine for gases comprising a shaft which turns about an axis of rotation, a worm mounted on said shaft having threads disposed in a helix and forming projections, the crests of said threads being disposed on a surface of revolution about said axis, a stationary casing surrounding said worm at least partially and in substantially leak-tight contact with at least part of the crest line of said threads, at least one pinion provided with teeth which are disposed in meshing engagement with said threads and rotate about an axis which is transverse with respect to the axis of rotation of said shaft, that face of said teeth which is exposed to the high pressure being disposed on a surface of revolution about said transverse axis, at least one low-pressure port being disposed on one side of said worm whilst a high-pressure port is disposed on the opposite side in the immediate vicinity of said pinion, said worm being provided on the same side as the high-pressure port with an extension which is such that the periphery thereof is disposed on a surface of revolution about the axis of rotation of said shaft and which cooperates in substantially leak-tight manner with said casing, and characterized in that the zone of said casing which cooperates in substantially leak-tight manner with said extension has in the direction parallel to the axis of rotation of said worm a maximum width in the vicinity of said high-pressure port.

iJnited States Patent [191 Zimmern [4 1 oer. 15, 1974 COMPRESSORS AND EXPANSION MACHINES OF THE WORM AND PINION TYPE [76] Inventor: Qernard Zimmern, c/o S. J Rudy 8 E 'MthSt, New York, NY. 16617 [22] Filed: Apr. 5, 1973 [21] Appl. No.: 348,159

Zimmern Zimmern 418/195 Primary ExaminerC. J. Husar Attorney, Agent, or Firm-Stephen J. Rudy 57 ABsTRAcT A compressor or expansion machine for gases comprising a shaft which turns about an axis of rotation, a worm mounted on said shaft having threads disposed in a helix and forming projections, the crests of said threads being disposed on a surface of revolution about said axis, a stationary casing surrounding said worm at least partially and in substantially leak-tight contact with at least part of the crest line of said threads, at least one pinion provided with teeth which are disposed in meshing engagement with said threads and rotate about an axis which is transverse with respect to the axis of rotation of said shaft, that face of said teeth which is exposed to the high pressure being disposed on a surface of revolution about said transverse axis, at least one low-pressure port being disposed on one side of said worm whilst a high-pressure port is disposed on the opposite side in the immediate vicinity of said pinion, said worm being provided on the same side as the high-pressure port with an extension which is such that the periphery thereof is disposed on a surface of revolution about the axis of rotation of said shaft and which cooperates in substantially leak-tight manner with said casing, and characterized in that the zone of said casing which cooperates in substantially leak-tight manner with said extension has in the direction parallel to the axis of rotation of said worm a maximum width in the vicinity of said high-pressure port.

2 Claims, 6 Drawing Figures Pmmnw 1 5 014 3 .841 806 COMPRESSORS AND EXPANSION MACHINES OF THE WORM AND PINION TYPE BACKGROUND OF THE- INVENTION As already disclosed in particular in French Pat. Nos. 1,287,593, 1,331,998, 1,586,832 and in French Pat. application No. 7209595, it is known to construct gas compressors or expansion machines of the type comprising a worm provided with a plurality of threads and rotatably mounted within a stationary casing, the crests of the threads being intended to cooperate with said casing and said threads being disposed in meshing engagement with at least one pinion provided with teeth disposed in meshing engagement with said threads, at least one low-pressure port being located on one side of the worm whilst a high-pressure port is located on the opposite side of said worm in the immediate vicinity of each pinion, said worm being extended on the highpressure side by a portion of revolution which is in leak-tight contact with said casing.

It has been found, however, that this arrangement gave rise to a high degree of friction by reason of the fact that provision is made in these machines for the injection of auxiliary liquid such as oil which ensures leaktightness, cooling and lubrication, thereby setting up at the periphery of the worm, between said worm and the casing, hydraulic friction forces which consume power and impair the power efficiency of the machine.

It would quite clearly be possible to reduce these friction forces by making provision at the points corresponding to the'leakage zones, that is to say along the thread crests or along the perimeter of the worm on the high-pressure side; for thin ridges which are fitted by grinding together with the casing with very small values of clearance while reducing the friction surfaces to a considerable extent, as isin any case achieved in a known manner in worm compressors of the Lysholm type.

This solution is nevertheless attended by a number of disadvantages. In the first place, it calls for highly accurate concentricity of the periphery of the worm with respect to the casing under penalty of substantial displacements off-centre and high values of clearance along the ridges. Moreover, these ridges are delicate and, if solid particles pass into the machine in spite of the filtering devices, said ridges are destroyed in the course of time and this results in leakage as well as a reduction in thermodynamic efficiency.

Finally, the rotating parts must be machined to very close tolerances or, if the method of grinding-in and self-adaptation of the worm within its casing is adopted, it then becomes difficult to ensure interchangeability of worms and casings.

The object of this invention is to provide an improved casing and worm relationship in a compressor whereby the hydraulic friction forces that would otherwise develop are substantially decreased and the efficiency of the machine is increased while at the same time a desirable leak tightness between the worm and the casing is maintained.

In accordance with the present invention, there is provided a compressor or expansion machine for gases comprising a shaft which turns about an axis of rotation, a worm mounted on said shaft and provided with a plurality of threads disposed in a helix and forming projections, the crests of said threads being disposed on a surface of revolution about said axis, a stationary casing surrounding said worm at least partially and in substantially leak-tight contact with at least part of the crest line of said threads, at least one pinion provided with teeth which are disposed in meshing engagement with said threads and rotate about an axis which is transverse with respect to the axis of rotation of said shaft, that face of said teeth which is exposed to the high pressure being disposed on a surface of revolution about said transverse axis, at least one low-pressure port being disposed on one side'of said worm whilst a high-pressure port is disposed on the opposite side in the immediate vicinity of said pinion, said worm being provided on the same side as the high-pressure port with an extension which is such that the periphery thereof is disposed on a surface of revolution about the axis of rotation of said shaft and which cooperates in substantially leak-tight manner with said casing, and characterized in that the zone of said casing which cooperates in substantially leak-tight manner with said extension has in the direction parallel to the axis of rotation of said worm a maximum width in the vicinity of said high-pressure port.

It has in fact been observed that this arrangement permits a very appreciable reduction in the hydraulic friction forces aforesaid while making it possible to retain between the worm and the casing substantial clearances which permit wide machining tolerances and BRIEF DESCRIPTION OF THE DRAWING A better understanding of the present invention will be obtained from a perusal of the accompanying drawings, in which:

FIG. 1 is a view taken partly in elevation and partly in cross-section, showing a worm in accordance with the present invention and a pinion which cooperates with said worm;

FIG. 2 is an elevation view of a half-casing which is intended to cooperate with the worm and two symmetrical pinions;

FIG. 3 is a sectional view taken along line 3-3 of FIG. 2 in which is added a sectional view of the worm in position within the half-casing; FIG. 3 is drawn to a larger scale than that of FIG. 2;

FIG. 4 is a sectional view taken along line 4-4 of FIG. 2;

FIG. 5 is a sectional view taken along line 55 of FIG. 2;

FIG. 6 is a graph in which the pressures within the casing are related to the width of the sealing strip.

DESCRIPTION OF PREFERRED EMBODIMENT There is shown in FIG. I a worm 1 provided with a plurality of threads such as the thread 2 and capable of rotating about the axis 3 in the direction of the arrow 7 when the machine operates as a compressor. The worm meshes with two symmetrical pinions; the reference numeral 4 designates one of the pinions aforesaid which is provided with teeth 5 and rotates about an axis represented in the figure by the point 6, in the direction of the arrow 8; provision is made for a second pinion which is disposed symmetrically but is not illustrated.

The directions of rotation are reversed when the machine operates as an expansion unit. The casing comprises a pair of opposed half-casings 9, only one of which is shown.

An elevation view of a half-casing 9 is shown in FIG. 2 and a sectional view of this latter as taken along line 33 of FIG. 2 is shown in FIG. 3, to which has been added the worm in its position of operation and its bearing-plates l and 11; the half-casing is shown in FIG. 4 in a first cross-section taken on line 4-4 of FIG. 2; and is shown in FIG. 5 in a further cross-section taken on line 5-5 of FIG. 2.

It is apparent that the bearing-plate carries antifriction bearings 13 which support the worm shaft 14 and that the bearing-plate 11 carries an antifriction bearing 15 which also supports said shaft; the suction inlet or low pressure ports are constituted by openings 16 formed in the bearing-plate 11.

An exhaust or high pressure port 17 is formed in the hemicylindrical cavity 18 of the half-casing. The pinions are disposed within recesses such as 20 which are formed in the casing in accordance with arrangements which are known per se or in accordance with French Pat. Application No. 7,209,937.

It will be noted. especially from FIGS. 2 and 3, that the surfacearea defining the hemicylindrical cavity 18 of each casing half is comprised of different regions or zones. The end zones 26 and 27 serve to accommodate and center the bearing plates 10 and 11. The cavity 18 of one half casing together with the other half provide a cylindrical cavity wherein the worm turns.

It can be understood that the necessary tightness of the compressor requires that the crests 19 of the worm threads be quite close to the opposed surface of the cylindrical cavity of the casing. Accordingly, when the compressor is running, some energy is wasted byway of viscous friction due to the thin layer of tightness and lubrication liquid. In the present invention, this waste is decreased by way of enlarging the clearance between worm thread and casing everywhere the tight closeness is not needed. To this end, different zones are provided in the cylindrical cavity of the casing, the respective diametersof which being different from each other.

Facing the crests I9, the zones 21 and 23 are provided on the hemicylindrical surface of each casing half; they are separated by the edge 22, which is helecoidal, the diameter of the zone 21 being slightly greater than that of zone 23. The zone 23 is in substantially leak-tight contact with the crests 19 of the worm threads.

The periphery of the worm is axially extended by a solid unthreaded cylindrical portion 30 at the high pressure side, as best seen in FIG. 1. Facing the cylindrical portion 30 of the worm, two zones 24 and 25 are provided on the said hemicylindrical surface, zone 25 being of a slightly greater diameter than zone 24. For clarification only, zone 24 is shown as hatched in the drawing so as to readily delimit it from the adjacent zones. Zone 24 is in substantially leak-tight contact with the solid portion of the worm. Zone 21 provides a substantial clearance with respect to the crests of the worm; and zone 25 provides a substantial clearance with respect to the solid portion 30.

Zones 24 and 25 are separated by the edge 31, zone 25 being slightly greater in diameter than zone 24. At the lower end, as best seen in FIG. 2, of zone 24, near the exhaust port 17, the pressure is high and the closeness between worm and casing must extend over a large width in order to obtain the desirable tightness. At the upper end (FIG. 2) of zone 24 a smaller width 1 is allowed to be provided because the pressure in this area has its lowest value.

It is apparent that the zone 24 is of maximum width in the vicinity of the high-pressure port 17 and of minimum width on the opposite side.

The width 1 in the position in FIG. 2 is shown in FIG. 6 as a function of its angular position a about the axis of the casing whilst the curve 42 shows the mean pressure which exists as a result of the compression within the worm threads opposite to said position when this latter travels through the angle of 180 of the halfcasing. It will also be noted that an aperture 50 connected to a passageway 51 formed in the casing and to an aperture 52 balances in a manner disclosed by the patent cited earlier the pressures developed at the level of the zone 25 and the suction pressure, and serves to return to the suction side any leakage which occurs between the surfaces 24 and 30.

As can be seen from FIG. 6, the two curves 43 and 42 are in substantially coincident relation.

In point of fact, it is known that the leakage between two substantially leak-tight contact surfaces is proportional to the pressure on each side of the sealing zone and inversely proportional to the length of said sealing zone.

By means of the foregoing arrangement in accordance with the present invention, practically constant leakage is ensured between the portion 30 of the worm and the portion24 of the casing but the surface 24 which is in substantially leak-tight contact with the worm has been reduced substantially by one-half with respect to the prior art in which said zone 24 was of constant width. This results in appreciable reduction in hydraulic friction forces since these-machines are provided with means known per se (and therefore not illustrated in the drawings) for the injection of auxiliary liquid for operation both as compressors and expansion machines.

I By way of example and in the case of a worm having a diameter of millimetres and rotating at 3,000 rpm, a clearance of 0.1 millimetre between the solid zone 30 of the worm and the zone 24, a length of 26 millimetres of the zone 24 and therefore of the solid portion 30 of the worm parallel to its axis and an oil having a viscosityof I50 SUS at 20, a mode of use of the apparatus as an air compressor delivering 4 cubic metres per minute at 7 bars and developing an effective horse power of approximately 34 b.h.p. by means of the known arrangements, there is a gain of approximately 2 b.h.p. without any change in output by virtue of the present arrangements. This appreciable gain represents about 5 percent of the total power but about 25 percent of losses due to all causes which affect the efficiency of the machine.

It should be noted that this arrangement is particularly simple and easy to obtain by direct casting of the zone 25.

It is also worthy of note that the clearance of 0.10 millimetre must be reduced to 0.02 0.03 millimetre when fine multiple ribs forming a labyrinth are employed instead of the solid portion 30.

As already described with reference to FIGS. 2 and 4, it is also possible to dispense with any Ieak-tight contact between the thread crests l9 and the casing throughout the zone 21 in which such a contact serves no useful purpose by reason of the fact that no compression takes place within the volumes formed between those threads which are located opposite to this zone.

The edge 22 coincides substantially with the position of the crest of a worm thread when the volume adjacent to said thread begins its compression.

An arrangement as just described also achieves a gain in power although this gain is appreciably lower than in the arrangement described in the case of the zone 24.

What is claimed is:

l. A compressor or expansion machine for gases comprising a shaft which turns about an axis of rotation, a worm mounted on said shaft and provided with a plurality of threads disposed in a helix and forming projections, the crests of said threads being disposed on a surface of revolution about said axis, a stationary casing surrounding said worm at least partially and in substantially leak-tight contact with at least part of the crest line of said threads, at least one pinion provided with teeth which are disposed in meshing engagement with said threads and rotate about an axis which is transverse with respect to the axis of rotation of said shaft, that face of said teeth which is exposed to the high pressure being disposed on a surface of revolution about said transverse axis, at least one low-pressure port being disposed on one side of said worm whilst a high-pressure port is disposed on the opposite side in the immediate vicinity of said pinion, said worm being provided on the same side as the high-pressure port with an extension which is such that the periphery thereof is disposed on a surface of revolution about the axis of rotation of said shaft and which cooperates in substantially leak-tight manner with said casing, and characterized in that the zone of said casing which cooperates in substantially leak-tight manner with said extension has in the direction parallel to the axis of rotation of said worm a maximum width in the vicinity of said high-pressure port.

2. A compressor or expansion machine in accordance with claim 1, characterized in that the zone of said casing which is in substantially leak-tight contact with the crests of said threads is limited to the zone of the casing in which the volume enclosed between the threads is at a pressure which is higher than the low pressure.

UNITED STATES PATENT OFFICE I I CERTIFICATE OF CORRECTION Patent No. 3,841,806 Dated October 15; 1974 Inventor) Bernard Z lmmern It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Applicant's address should read I 27 rue Delaborde're Neuil ly-sur-Seine (Hauts de Seine) France (SEAL) Attest:

McCOY M. GIBSON JR. Attesting Officer 0. MARSHALL DANN Commissioner of Patents ORM po'wso (w'ss) USCOMM-DC 60376-P69 U 5 GOVERNMENT FRlNTlNG OFFICE: 669-930 

1. A compressor or expansion machine for gases comprising a shaft which turns about an axis of rotation, a worm mounted oN said shaft and provided with a plurality of threads disposed in a helix and forming projections, the crests of said threads being disposed on a surface of revolution about said axis, a stationary casing surrounding said worm at least partially and in substantially leak-tight contact with at least part of the crest line of said threads, at least one pinion provided with teeth which are disposed in meshing engagement with said threads and rotate about an axis which is transverse with respect to the axis of rotation of said shaft, that face of said teeth which is exposed to the high pressure being disposed on a surface of revolution about said transverse axis, at least one low-pressure port being disposed on one side of said worm whilst a highpressure port is disposed on the opposite side in the immediate vicinity of said pinion, said worm being provided on the same side as the high-pressure port with an extension which is such that the periphery thereof is disposed on a surface of revolution about the axis of rotation of said shaft and which cooperates in substantially leak-tight manner with said casing, and characterized in that the zone of said casing which cooperates in substantially leak-tight manner with said extension has in the direction parallel to the axis of rotation of said worm a maximum width in the vicinity of said high-pressure port.
 2. A compressor or expansion machine in accordance with claim 1, characterized in that the zone of said casing which is in substantially leak-tight contact with the crests of said threads is limited to the zone of the casing in which the volume enclosed between the threads is at a pressure which is higher than the low pressure. 